This is an excerpt from MS Douce 257
(England, 1381)
The original source can be found at
MedievalCookery.com
Longe de buf. Nym þe tonge of þe reþer & schalde, & schawe yt wel & ryt clene, & seþ yt; & seþe nym a broche, & larde yt wyþ lardons and wyþ | clowys gelofre, & do it rostyng. & drop yt, wel yrostyd, wyþ olkys of eyrin, & dresse it forþe.
Recipes with similar titles:
longe bef (A Noble Boke off Cookry)
XLIII - FOR TO MAKE LONGE DE BUF (Forme of Cury)
Lange de beof (Liber cure cocorum [Sloane MS 1986])